The present invention relates to a swash plate type variable displacement compressor.
Japanese Unexamined Patent Application Publication No. 52-131204 discloses a swash plate type variable displacement compressor (hereinafter, referred to as the compressor). The compressor includes a housing that has therein a suction chamber, a discharge chamber, a swash plate chamber and a plurality of cylinder bores. A drive shaft is rotatably supported in the housing. The swash plate chamber has therein a swash plate that is rotatable with the drive shaft. The swash plate is of an annular shape having an insertion hole at the center thereof through which the drive shaft is passed. A link mechanism that allows a change in the inclination angle of the swash plate is provided between the drive shaft and the swash plate. The angle of inclination of the swash plate herein refers to an angle of the swash plate with respect to a plane extending perpendicular to the axis of rotation of the drive shaft.
A piston is received in each cylinder bore so that the piston is reciprocally movable in the cylinder bore. The compressor further includes a conversion mechanism that converts the rotation of the swash plate into a reciprocal movement of the piston in the cylinder bore for a length of stroke determined by the inclination angle of the swash plate, an actuator that changes the inclination angle of the swash plate and a control mechanism that controls the actuator.
The link mechanism includes a lug member and an arm. The lug member is fixed on the drive shaft in the front of the swash plate chamber. The arm is connected to the lug member via a connecting pin so as to be swingable with the lug member and the swash plate. The arm transmits the rotation of the lug member to the swash plate and allows a change in the inclination angle of the swash plate while the top dead center of the swash plate being substantially maintained.
The actuator includes the lug member and a movable body that is engaged integrally rotatably with the swash plate and is movable in the direction of axis of rotation of the drive shaft so as to change the inclination angle of the swash plate. Specifically, the lug member has therein a cylinder chamber that has a shape of a cylinder that is coaxial with the axis of rotation of the drive shaft and in which the movable body is movable. In such a structure in which the cylinder chamber is defined by the movable body, a pressure control chamber is formed in the cylinder chamber that controls the movement of the movable body with the pressure in the pressure control chamber. The swash plate has in the insertion hole thereof a hinge ball. The swash plate is mounted on the drive shaft through the hinge ball so that the swash plate is inclinable about the drive shaft. The rear end of the movable body is in contact with the hinge ball. The hinge ball has at the rear end thereof a pressure spring that urges the hinge ball in the direction that increases the inclination angle of the swash plate.
The control mechanism includes control passages and a control valve. Specifically, the control passages include a pressure-changing passage that communicates with the pressure control chamber, a low-pressure passage that communicates with the suction chamber and the swash plate chamber, and a high-pressure passage that communicates with the discharge chamber. A part of the pressure-changing passage is formed in the drive shaft. The control valve controls the opening of the pressure-changing passage, the low-pressure passage and the high-pressure passage. In other words, the control valve controls the communication between the pressure-changing passage and the low-pressure passage or between the pressure-changing passage and the high-pressure passage.
In the compressor, when the control valve permits communication between the pressure-changing passage and the high-pressure passage, the pressure in the pressure control chamber becomes higher than the pressure in the swash plate chamber. Accordingly, the movable body of the actuator is moved away from the lug member and pushes the hinge ball rearward in the swash plate chamber, which decreases the inclination angle of the swash plate. Therefore, the stroke length of the pistons is decreased and the displacement of the compressor also is decreased, accordingly. When the control valve permits communication between the pressure-changing passage and the low-pressure passage, on the other hand, the pressure in the pressure control chamber is decreased to approximately the same pressure as that of the swash plate chamber. Accordingly, the movable body of the actuator is moved toward the lug member. In this case, the hinge ball moves with the movable body because of the urging force of the pressure spring. Accordingly, the inclination angle of the swash plate is increased, and the stroke length of the pistons and hence the displacement of the compressor are increased.
The compressor of the above type is required to change the inclination angle of the swash plate quickly in response to a change in the driving condition of the vehicle on which the compressor is mounted. In order to meet such requirement, the diameter of the pressure control chamber may be increased to move the movable body with an increased thrust force, without increasing the pressure in the pressure control chamber. In this case, however, it is difficult to increase the diameter of the cylinder chamber in the lug member due to the presence of the link mechanism between the drive shaft and the swash plate and, therefore it is difficult to increase the diameter of the pressure control chamber.
Furthermore, in the compressor, the thrust force generated during the operation of the compressor acts on the link mechanism. Therefore, the link mechanism is required to adequately withstand the thrust force. If the diameter of the cylinder chamber is increased by disposing the cylinder chamber closer to the piston than to the thrust bearing, the compressor need be made longer in the axial direction.
The present invention that has been made in view of the above-identified circumstances is directed to providing a swash plate type variable displacement compressor that has good controllability, withstands the thrust force and may be made smaller in the axial direction.